Process for the deposition of metallic aluminum



United States Patent 3,214,238 PROCESS FOR THE DEPOSITION 0F METALLIC ALUMINUM Leslie D. McGraw, Columbus, Ohio, assignor, by mesne assignments, to National Steel Corporation, Pittsburgh, Pa., a corporation of Delaware No Drawing. Filed Dec. 14, 1961, Ser. No. 159,447 6 Claims. (Cl. 117-113) This invention broadly relates to the deposition of metals without the use of electric current and in some of its more specific variants to a novel process for the deposition of metallic aluminum-containing material on a substrate and to the resultant novel product thus produced.

The invention will be described and illustrated hereinafter with reference to the nonelectrolytic deposition of metallic aluminum-containing material on a substrate. However, it is understood that the principles of the invention are applicable to the nonelectrolytic deposition of other suitable coating metals or alloys.

Aluminum has been deposited heretofore by nonelectrolytic processes. For instance, one prior art process involves applying a coating of aluminum hydride on a base material in a nitrogen atmosphere, and then subjecting the coated base material while in the nitrogen atmosphere to an elevated temperature for decomposing the aluminum hydride and producing a metallic aluminum coating thereon. However, the above and other prior art processes for the nonelectrolytic deposition of aluminum have serious limitations and disadvantages which render them generally unsatisfactory in some respect.

It is an object of the present invention to provide a novel nonelectrolytic process for the deposition of metals.

It is a further object of the present invention to provide a novel nonelectrolytic process for the deposition of a coating metal on a substrate and to provide the resultant novel product.

It is still a further object of the present invention to provide a novel nonelectrolytic process for the deposition of an aluminum-containing material.

It is still a further object of the present invention to provide a novel nonelectrolytic process for the deposition of a metallic aluminum-containing material on a substrate and to provide the resultant novel product.

It is still a further object of the present invention to provide a novel nonelectrolytic process for plating aluminum ona metallic substrate and to provide the resultant aluminum plated product.

' Still other objects and advantages of the present invention will be apparent to those skilled in the art upon reference to the following detailed description and the examples.

In accordance with one important variant of the invention, a metallic aluminum-containing material is deposited on a substrate by bringing it into intimate contact with a composition comprising a substance that yields metallic aluminum selected from the group consisting of aluminum halohydrides, organic complexes of aluminum halohydrides and mixtures thereof. The rate of deposition may be increased by heating to an elevated temperature to produce decomposition products including metallic aluminum, and the metallic aluminum while thus being produced may be deposited on the substrate in the form of a coating.

The aluminum halohydrides suitable for practicing the present invention may include compounds of the general formula AlH X where X is halogen, m and n each have a numerical value of at least one, and m+n are equal to three. Thus, in the foregoing general formula the atomic ratio of Al to H is between 1:1 and 1:2, the atomic ratio of Al to X is between 1:2 and 1:1, and the atomic ratio of Al to H+X is 1:3. Specific examples of aluminum halohydrides include AlHX AlH X, and mixtures thereof such as Al H X which may be written as AlH X for the purpose of this discussion. Chloride is preferred over other halogens in most instances, but bromine also usually gives very good results.

The stability of the foregoing aluminum halohydrides may be enhanced when this is desirable by preparing a coordinate covalent complex thereof. The complexes may be prepared by reacting the aluminum halohydride with organic compounds which are known to be capable of acting as Lewis bases such as ethers and other oxygencontaining organic compounds, or other compounds containing a functional group which is capable of allowing the complexing of aluminum halohydride such as organic compounds containing a divalent sulfur atom including the thioethers, organic compounds containing a trivalent nitrogen atom such as amines, and organic compounds containing a trivalent phosphorus atom. It is usually preferred that the complex be an etherate. A wide variety of ethers may be employed in forming the etherate such as ethyl, propyl, butyl, etc., and ethers in general wherein the organic groups attached to the oxygen atom contain, for example, about 1 to 8-20 carbon atoms. The ether may contain an aromatic group such as methylphenyl ether, ethylphenyl ether, diphenyl ether, etc. In some instances, other functional groups than the ether linkage may be present in the molecule such as in the compound ethoxyethyltrimethyl ammonium chloride. Ethers containing a plurality of ether linkages also may be used, such as diethyleneglycol diethylether.

If desired, aluminum halide may be present in the composition as free aluminum halide, or preferably as an organic complex of an aluminum halide. The organic coordinate covalent complexing agents for the aluminum halide are the same as discussed above for the aluminum halohydrides, and, similarly, the preferred complexing agent is an ether of the types discussed above. If desired, the plating composition may include a mixture of the aluminum halohydride and the aluminum halide, each in free or complexed form, or mixtures thereof. Preferably, the aluminum halide is aluminum chloride, but aluminum bromide also often gives excellent results.

The above described composition is brought into intimate contact with the substrate on which metallic aluminum-containing material is to be deposited at a temperature to produce products including metallic aluminum which deposit on the substrate. This may be conveniently accomplished by preparing a bath comprising the plating composition, immersing the substrate into the bath, and then heating the bath to produce products including metallic aluminum which deposit on the sub strate.

In many instances, the above described plating compositions are liquid at temperatures below the point at which metallic aluminum is deposited. Thus, the composition may be heated to slightly above the melting point, the substrate to be plated immersed in the resultant bath, and then the heating of the bath continued up to the point at which metallic aluminum is deposited or to some suitable higher temperature. In instances where aluminum is deposited below the melting point of the bath, then the composition may be first dissolved in a suitable solvent or suflicient solvent provided to assure a working fluidity at a temperature sufiiciently low to prevent a substantial amount of aluminum from depositing. Examples of suitable solvents will vary with the specific composition being used, but organic solvents for aluminum chloride such as ether, or a mixture of ethers of the types above discussed are usually satisfactory. Where a solvent is used to provide a working fluidity for the bath, the solvent may be added in an amount to produce a liquid plating composition at a temperature sufficiently low to prevent a substantial amount of aluminum from depositing, the substrate is immersed therein and then the composition is heated until products including metallic aluminum are formed and metallic aluminum is deposited on the substrate.

While it is usually preferred that a plating bath be heated with the substrate immersed therein to a temperature at which metallic aluminum is deposited, this may not always be necessary. For instance, the plating bath may be maintained in the liquid state below a temperature at which a substantial amount of aluminum is deposited and a substrate which has been heated to a temperature at least as high as that at which aluminum is deposited is immersed therein. This results in heating of the solution immediately adjacent the substrate with accompanying deposition of metallic aluminum. Still other variants may be used for bringing the plating composition into intimate contact with the substrate at a temperature at which aluminum is deposited.

The temperature at which the plating compositions described herein deposit aluminum may vary somewhat. It is only necessary that the plating composition be in contact with the substrate at a temperature at which aluminum is deposited and this may be accomplished by any convenient method. For instance, the composition may be heated from a temperature below the point at which a large amount of aluminum is deposited to a temperature which is at or above the point at which aluminum is deposited, while in intimate contact with the substrate to be plated. Usually, heating at temperatures between about 20 C. and about 150 C. is satisfactory when the aluminum halohydride is aluminum dichlorohydride or aluminum chlorohydride in the form of the etherate and in the presence of aluminum chloride etherate.

A wide variety of substrates may be plated with metallic aluminum-containing material in accordance with the teachings of the present invention. Specific examples of substrates include metals such as ferrous metal, brass, copper, aluminum, etc. If desired, nonmetallic substrates such as plastics, wallboard, wood, paper, paperboard and equivalent substances which are capable of withstanding the relatively low temperatures at which the plating composition deposits aluminum may be used as substrates. The substrate to be plated should be free of foreign matter which would prevent adherence of the metallic aluminum for best results. The term substrate is used herein to refer to a basis material on which the coating material may be deposited. The substrate may vary widely in both form and composition. For instance, the substrate may be in the form of sheets, rods, bars, blocks, spheres, irregularly shaped articles, etc., and it may be composed or partially composed of metal, organic plastic materials, ceramic material, etc. Preferably, the substrate is formed of a metal such as ferrous metal and alloys of iron, brass, copper, etc.

The preparation of aluminum halohydrides is well known, and a number of methods may be used. Preferably, aluminum chloride is dissolved in an organic solvent such as diethyl ether and then an active hydrogen-containing compound such as aluminum hydride, sodium hydride, potassium hydride, calcium hydride or lithium aluminum hydride is added thereto in the calculated quantity to provide the desired amount of active hydrogen in the resultant composition. For instance, the compound may be added in the calculated amount to react with the aluminum chloride and produce aluminum dichlorohydride, aluminum chlorohydride, Al I-I Cl or in a smaller amount so as to have one or more of these substances present in excess aluminum chloride or its complex. When aluminum hydride is reacted with the aluminum chloride, the molar ratio may be between 1 AlH :O.S AlCl and 1 AlH :22 A101 and preferably 1 AlH z2 A101 and 1 AlH ;ll A101 in most instances. Other metal hydrides may be used in equivalent amounts based on active hydrogen content.

Subsequent to the addition of the active hydrogen-containing compound to the ether solution of aluminum chloride, the excess ether may be evaporated by heating and/ or by aeration. The ether solution often may be used as the plating bath and especially in instances where the bath deposits aluminum at a low temperature. In instances where the bath deposits aluminum at a temperature substantially above the melting point, then the ether may be boiled oil, the composition heated to its melting point, the substrate immersed therein and then the heating continued until a temperature is reached at which aluminum is deposited Where the aluminum halohydride is prepared in the presence of ether, then the etherate is formed and the composition is actually an etherate of aluminum halohydride, which is usually preferred.

While the process of the present invention has been described as being suitable for the plating of metallic aluminum-containing materials, it is understood that the principles of the invention may be applied to the plating of other metals b-y nonelectrolytic processes. For instance, metals other than aluminum may be deposited in accordance with the teachings of the invention where a halohydride of the metal is available which may be decomposed in the presence of the substrate in accordance with the teachings of the invention.

The foregoing detailed description and the following specific examples are for purposes of illustration only, and are not intended as being limiting to the spirit or scope of the appended claims.

Example I The monoetherate of aluminum dichlorohydride was prepared by dissolving aluminum chloride in diethyl ether and treating the solution with lithium aluminum hydride in the calculated amount to produce AlHCl Excess ether was then evaporated from the resultant product.

The above prepared composition was heated slightly above the melting point, a clean brass article submerged in the resultant liquid and the heating was continued until a temperature was reached at which products including metallic aluminum were produced. The temperature was about 110 C., at which temperature metallic aluminum plated on the brass article. Thereafter, the aluminum plated brass article was removed from the bath, washed in water and examined. The aluminum coating was uniform, adherent and bright.

The above procedure was repeated for ferrous metal articles and aluminum articles with substantially identical results being observed. Also, plastics or other nonmetallic substrates capable of withstanding the 110 C. decomposition temperature could be substituted for the above metals to thereby obtain an aluminum plated product.

Example II To a dilute diethyl ether solution of aluminum chloride was added lithium aluminum hydride in the calculated amount to produce Al H Cl followed by removal of some but not all of the excess ether. The resultant composition was maintained in the liquid state at a temperature below the decomposition point.

A clean brass article was submerged in the liquid composition above prepared, and then the temperature was raised slowly up to where products including metallic aluminum were produced, which occurred at about C. The aluminum plated on the brass article in the form of a tightly adherent coating and the results obtained were substantially the same as recorded in Example I.

Other metallic substrates such as ferrous metal and aluminum gave the same results as recorded in Example II. Also, plastics or other nonmetallic substrates which were stable at the bath temperature of 90 C. could be substituted.

Example III Lithium aluminum hydride was added to a dilute diethyl ether solution of aluminum chloride in an amount calculated to produce AlH Cl. The resultant ether solution was found to have a deposition point at which products including metallic aluminum were produced between room temperature and about 70 C., and it was not possible to remove all of the ether by evaporation without partially decomposing the bath.

A composition as prepared above and containing sufficient ether to maintain the composition liquid at room temperature was used for the plating of aluminum on a brass article. The brass article was submerged in the bath, and the temperature gradually raised to approximately 70 C. Aluminum plated out on the brass article with substantially the same results being obtained as noted above in Example I. Also, other metallic substrates such as ferrous metal, aluminum, etc. could be substituted for the brass, or organic substrates which are stable at 70 C. could be substituted.

Example IV An etherate of aluminum chloride was prepared by dissolving aluminum chloride in ether, and then evaporating the excess ether. The resultant monoetherate of aluminum chloride was used in preparing baths from each of the etherates of the aluminum chlorohydrides prepared in accordance with Examples I, II and III, using 2 mols of the etherate of aluminum chlorohydride for each 3.8 mols of the etherate of aluminum chloride.

The resultant baths were used in plating aluminum in the manner set forth in Examples 1, II and III, with substantially identical results being obtained. Since the baths were in the liquid state a few degrees above room temperature, it was possible to effect the plating operation by melting the compositions, immersing the articles to be plated in the liquids, and then heating to a temperature at which products including metallic aluminum are formed to deposit the aluminum.

What is claimed is:

1. A process for depositing metallic aluminum-containing material on a substrate comprising intimately contacting the substrate with a liquid composition comprising at least one etherate of an aluminum halohydride which yields metallic aluminum, the deposition of the aluminumcontaining material being induced by bringing the liquid composition into contact with the substrate at a temperature to produce products including metallic aluminum and metallic aluminum thus produced being deposited on the substrate.

2. A process for depositing metallic aluminum-containing material on a substrate comprising intimately contacting the substrate with a liquid composition comprising at least one etherate of an aluminum chlorohydride which yields metallic aluminum, the deposition of the aluminumcontaining material being induced by bringing the liquid composition into contact with the substrate at a temperature to produce products including metallic aluminum and metallic aluminum thus produced being deposited on the substrate.

3. A process for depositing metallic aluminum-containing material on a substrate comprising intimately contacting the substrate with a liquid composition comprising at least one etherate of an aluminum bromohydride which yields metallic aluminum, the deposition of the aluminumcontaining material being induced by bringing the liquid composition into contact with the substrate at a temperature to produce products including metallic aluminum and metallic aluminum thus produced being deposited on the substrate.

4. A process for depositing metallic aluminum-containing material on a substrate comprising immersing the substrate in a liquid composition comprising at least one etherate of an aluminum halohydride which yields metallic aluminum, and heating the composition while in contact with the substrate to a temperature to produce products including metallic aluminum and deposit metallic aluminum thus produced on the substrate.

5. A process for depositing metallic aluminum-containing material on a substrate comprising immersing the substrate in a liquid composition comprising at least one etherate of an aluminum chlorohydride which yields metallic aluminum, and heating the composition while in contact with the substrate to a temperature to produce products including metallic aluminum and deposit metallic aluminum thus produced on the substrate.

6. A process for depositing metallic aluminum-containing material on a substrate comprising immersing the substrate in a liquid composition comprising at least one etherate of an aluminum bromohydride which yields metallic aluminum, and heating the composition while in contact with the substrate to a temperature to produce products including metallic aluminum and deposit metallic aluminum thus produced on the substrate.

References Cited by the Examiner UNITED STATES PATENTS 2,523,461 9/50 Young et al 117-130 X 2,619,433 11/52 Davis et al 117-107 2,843,474 7/58 Ziegler et al 7568 2,847,320 8/58 Bulloff 117-107 2,880,115 3/59 Drummond 117-107 2,918,392 12/59 Beller 117-1072 X 2,992,248 7/ 61 Pearson 260-429 FOREIGN PATENTS 1,156,065 12/57 France.

1,072,914 l/ Germany.

1,084,542 6/60 Germany.

OTHER REFERENCES Wiberg: Z. Naturforsch, vol. 6b (1951), pp. 460, 461.

Wiberg et al.: Z. Naturforsch, vol. 6b (1951), pp. 333, 334.

Wiberg et al.: Zeitschrift fiir anorg. und allgemene Chemie vol. 272, p. 226.

RICHARD D. NEVIUS, Primary Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,214,288 October 26, 1965 Leslie D. McGraw It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 2, line 4, for "Chloride is" read Chlorine is line 37, for "halohydrides, and," read halohydrides and,

Signed and sealed this 4th day of October 1966.

(SEAL) Attest:

ERNEST W. SW'IDER EDWARD J. BRENNER Attesting Officer Commissioner of Patents 

1. A PROCESS FOR DEPOSITING METALLIC ALUMINUM-CONTAINING MATERIAL ON A SUBSTRATE COMPRISING INTIMATELY CONTACTING THE SUBSTATE WITH A LIQUID COMPOSITION COMPRISING AT LEAST ONE ETHERATE OF AN ALUMINUM HALOHYDRIDE WHICH YIELDS METALLIC ALUMINUM, THE DEPOSITION OF THE ALUMINUMCONTAINING MATERIAL BEING INDUCED BY BRINGING THE LIQUID COMPOSITION INTO CONTACT WITH THE SUBSTRATE AT A TEMPERATURE TO PRODUCE PRODUCTS INCLUDING METALLIC ALUMINUM AND METALLIC ALUMINUM THUS PRODUCED BEING DEPOSITED ON THE SUBSTRATE. 